CUDA allows the GPU on the graphics card to be used for general computing.
System info:
Installation instructions here: https://docs.nvidia.com/cuda/cuda-installation-guide-linux/index.html
But then I found these instructions and followed them: https://askubuntu.com/questions/1288672/how-do-you-install-cuda-11-on-ubuntu-20-10-and-verify-the-installation
I didn’t do the verification step at the end, but after a reboot following installation I can now select CUDA as the Cycles render device in Blender.